The application relates generally to semiconductor processing equipment and particularly to measuring the temperature of pedestals and susceptors with optical techniques at relatively low temperatures.
Semiconductor processing equipment is used in the deposition, patterning, and treatment of thin films and coatings. A conventional substrate processing chamber provides a pedestal or some equivalent way of supporting the substrate for processing. Heat may be provided to the substrate by heating the pedestal with a resistive mechanism or by using heat lamps to heat the pedestal and substrate. Lamps are typically located outside the processing chamber. The light is allowed in through viewports or domes made of highly optically transmissive material such as quartz. Quartz is also attractive due to the low coefficient of thermal expansion and high melting temperature.
High temperature processes often use quartz domes and external lamps to quickly raise the temperature of the substrate to a processing temperature. Illustrative examples of processes and associated process chambers which employ such architectures are epitaxial film growth (often referred to as EPI) and rapid thermal processing (RTP). A pedestal is often referred to as a susceptor in processes which use lamps for heating. Processed film characteristics (e.g. film thickness, density, dopant density etc.) in these processes, as well as other processes, can be sensitive to substrate temperature.
Traditional methods of determining temperature involve thermocouples mounted in various locations inside the processing chamber. Difficulties with thermocouples involve drifts in the temperature measurement due, in part, to degradation of the thermocouple joint or a change in position. The substrate temperature may be monitored by aiming a pyrometer through a top quartz dome at the substrate generally from above. Another method of measuring the substrate temperature consists of aiming a pyrometer at the underside of the susceptor through a bottom quartz dome forming the underside of the processing chamber. The temperature of the substrate can be correlated to the temperature of the susceptor in a lookup table or using a correlation factor or other calculation.
Traditional high temperature processes involve substrate temperatures in the range 650° C. to 1150° C. Some processes are being used or are under development involving substrate temperatures in the range 300° C. to 650° C. One such deposition process involves the formation of a silicon carbide layer on a silicon substrate. Using a pyrometer at these lower temperatures is difficult due to the much smaller amount of light emanating from the substrate or susceptor. Background light coming from other areas of the chamber or even reflected light originating from the heat lamps can result in a poor substrate temperature reading.
Therefore, what is needed is a system and method for reliably and quickly measuring substrate temperature even at low temperatures.